Sorry, I'm not sure I understand. Isn't the hand animation always played when placing blocks?
Sorry, I did a Google search for this bug but I guess I should have searched within Jira! Is there a way to mark this post as a duplicate or to delete it?
It's not, this one's about water and that bug is related to dye.
Slabs were added later, in Minecraft Beta.
It could be partially for command block reasons, but probably's mostly for the capability to be right-clicked also for coloring the text of the sign.
Thanks for the explanation! While this and MC-166885 are related, I still wouldn't consider them duplicates.